98
M. Yamanaka
Table 4.8 Deduced pulsed width and measured subcriticality in dollar units by fuel rod substitution
and control rod insertion (Ref. [12])
Case
# of fuel
rods
Rod Insertion
pattern
Pulsed width in
optical fiber and
(BF 3 ) detectors [s]
Subcriticality [$] (methodology)
II-1
25
C1, C2, C3
(2.10 ± 0.05)E-04
((4.30 ± 0.20)E-04)
1.20 ± 0.03 (control rod worth)
II-2
25
C1, C2, C3,
S4
(1.25 ± 0.05)E-04
((3.10 ± 0.20)E-04)
2.01 ± 0.06 (control rod worth)
II-3
25
C1, C2, C3,
S4, S5, S6
(1.00 ± 0.05)E-04
((2.90 ± 0.20)E-04)
2.66 ± 0.07 (control rod worth)
II-4
21
–
(1.00 ± 0.05)E-04
((2.70 ± 0.10)E-04)
3.32 ± 0.02 (area ratio method)
II-5
21
C1, C2, S4,
S6
(5.12 ± 0.25)E-05
((2.20 ± 0.05)E-04)
6.13 ± 0.05 (area ratio method)
II-6
19
–
(5.00 ± 0.42)E-05
((2.75 ± 0.02)E-04)
6.80 ± 0.05 (area ratio method)
II-7
19
C1, C2, S4,
S6
(5.00 ± 0.42)E-05
((2.60 ± 0.02)E-04)
10.16 ± 0.09 (area ratio method)
4.2.3 Results and Discussion
4.2.3.1 Parameters in Rossi-α Method
The PNS experiments were carried out for the neutron noise analyses by the Rossi-α
method. Moreover, the PNS histogram was obtained to acquire α values to supplement neutron noise analyses, as shown in Fig. 4.2. To obtain the intensity of the
second term in Eq. (4.23), fitting based on Eq. (4.24) is required in the region where
Fig. 4.2 PNS histogram of
optical fiber detector in Case
II-1 (Ref. [12])
0.00
0.01
0.02
0.03
0.04
0.05
10
1
10
2
10
3
10
4
10
5
Count rate [cps]
Time [s]
0